Apparatus and method for outputting heart sounds

ABSTRACT

An apparatus for outputting heart sounds includes an implantable system and an external system. The implantable system includes a sensor for generating sensed signals representing detected heart sounds, an interface circuit and a control circuit for receiving the sensed signals, generating data representing the heart sounds therefrom, and transmitting the data to the external system via the interface circuit. The external system includes an interface circuit for communicating with the implantable system, and a control circuit for receiving the data representing the heart sounds and for generating control signals that cause an output device to generate outputs representing the sounds. The implantable system may also include a sensor(s) for detecting cardiac electrical signals. In this case, outputs representing the cardiac electrical signals are also output.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/037,276,filed on Jan. 18, 2005, which is a continuation of application Ser. No.09/833,229, filed on Apr. 11, 2001, now U.S. Pat. No. 7,052,466, thespecification of which is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of cardiacmonitoring, and more particularly relates to detecting heart soundsusing an implanted sensor, transmitting data indicative of the heartsounds to an external system, and outputting the heart sound data.

BACKGROUND

Cardiac pacemakers generally provide functions including sensingelectrical signals generated by the heart, controlling stimulation ofexcitable tissues in the heart, sensing the response of the heart tosuch stimulation, and responding to inadequate or inappropriate stimulusor response (e.g., dysrhythmia) to deliver therapeutic stimuli to theheart. Some existing cardiac pacemakers also function to communicatewith an external programmer device to support a variety of monitoring,diagnostic and configuration functions.

Certain cardiac pacemakers include an internal accelerometer formeasuring the level of activity of the patient (e.g., movement caused bywalking around, or by muscle twitches). Such pacemakers process (e.g.,filter) the accelerometer signals to reduce noise interfering with themeasurement of the patient's activity, such as the sounds generated bythe heart itself, and then use the processed signals as inputs toalgorithms for generating the signals used to control the stimulation ofthe heart. For example, if accelerometer signals indicate that a patientis walking briskly, the pacemaker may stimulate the heart to beat at afaster rate (often subject to an upper rate limit) than when the patientis at rest. While the accelerometer signal is used internally to controlthe heart rate, this signal is not transmitted by the pacemaker to anexternal programmer for subsequent display on a display device. Thus,the accelerometer signal itself is an internal signal which is notoutput to the user.

A common method of diagnosing heart problems involves comparing theelectrical operation of the heart to its mechanical operation, andidentifying electrical-mechanical disassociation. Typically, a physicianlistens to a patient's heart using a stethoscope placed on the surfaceof the patient's body, and compares the heart sounds to anelectrocardiograph (ECG) trace generated by an ECG machine coupled toprobes placed on the patient's chest. This method suffers from severaldisadvantages, including the need to use the stethoscope, the effect ofvarious factors (e.g., the placement of the stethoscope, body fat, etc.)on the heart sounds, the need to electrically couple ECG probes to thepatient's chest, the difficulties faced by the physician in accuratelycomparing the sounds heard using the stethoscope to the traces displayedby the ECG machine, and the relatively high level of skill needed toperform this comparison (especially if a physician is not available).This method also does not continuously monitor for electrical-mechanicaldisassociation, thus making it difficult to detect disassociationoccurring between visits to the physician, and does not provide theability to produce a written record showing a detected disassociation.

Thus, it would be desirable to provide a method and apparatus foroutputting heart sounds, and/or for comparing electrical operation ofthe heart to mechanical operation of the heart, that overcome one ormore of the above-described disadvantages.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an implantable system includesa sensor for detecting heart sounds and generating sensed signalsrepresentative thereof, an interface circuit for communicating with anexternal system, and a control circuit coupled to the sensor and theinterface circuit. The control circuit receives the sensed signals,generates data representative of the heart sounds therefrom, andtransmits the data to the external system via the interface circuit. Thesensor, interface circuit and control circuit are implantable. Inanother aspect, an implantable system also includes a second sensor fordetecting cardiac electrical signals and generating second sensedsignals representative thereof, and the control circuit also receivesthe second sensed signals, generates second data representative of thecardiac electrical signals therefrom, and transmits the second data tothe external system. In another aspect, an implantable system alsoincludes a third implantable sensor for detecting second cardiacelectrical signals and generating third sensed signals representativethereof, and the control circuit receives the third sensed signals,generates third data representative of the second cardiac electricalsignals therefrom, and transmits the third data to the external system.

According to another aspect, an external system includes an interfacecircuit to communicate with an implanted system, an output device, and acontrol circuit coupled to the interface circuit and output device. Thecontrol circuit receives data representing heart sounds detected by theimplanted system, and generates control signals that, when applied tothe output device, cause the output device to generate outputs whichrepresent the heart sounds. In another aspect, a control circuit alsoreceives data representing cardiac electrical signals from the implantedsystem, and generates control signals to cause the output device togenerate outputs representing the heart sounds and cardiac electricalsignals. In another aspect, a control circuit receives data representingsecond cardiac electrical signals from the implanted system, and causesthe output device to generate outputs representing the heart sounds andthe two cardiac electrical signals.

According to another aspect, a method of outputting heart soundsincludes detecting heart sounds using an implanted sensor, andtransmitting data representing the heart sounds to an external system.In another aspect, a method also includes detecting cardiac electricalsignals using an implanted sensor and transmitting data representing thecardiac electrical signals to an external device. In another aspect, amethod also includes detecting second cardiac electrical signals usingan implanted sensor, and also transmitting data representing the secondcardiac electrical signals to an external device.

According to another aspect, a method of outputting heart soundsincludes receiving data representing heart sounds detected by animplanted system, generating control signals using the data, andapplying the control signals to an output device to cause the outputdevice to generate outputs which represent the heart sounds. In anotheraspect, a method also includes receiving second data representingcardiac electrical signals from the implanted system, and generating thecontrol signals using the second data to cause the outputs generated bythe output device to represent the cardiac signals. In another aspect, amethod also includes receiving third data representing second cardiacelectrical signals from the implanted system, and generating the controlsignals using the third data to cause the outputs to also represent thesecond cardiac signals.

Other aspects of the present invention will be apparent upon reading thefollowing detailed description of the invention and viewing the drawingsthat form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary system for detecting heartsounds using an implanted sensor, transmitting data representing theheart sounds to an external system, and outputting the heart sound data,according to one embodiment of the invention;

FIG. 2 is a flow chart illustrating one embodiment of the processingperformed by the controller of the implantable device shown in FIG. 1;

FIG. 3 is a flow chart illustrating one embodiment of the processingperformed by the controller of the external device shown in FIG. 1;

FIG. 4 is a block diagram illustrating one embodiment of the signalprocessing performed on the heart sound signals detected by theexemplary system shown in FIG. 1;

FIG. 5 is an exemplary output display screen that is generated by theexternal device shown in FIG. 1;

FIG. 6 is another exemplary output display screen that is generated bythe external device shown in FIG. 1;

FIG. 7 is a flow chart showing another embodiment of the processingperformed by the controller of the implantable device shown in FIG. 1,including a logbook feature; and

FIG. 8 is a block diagram of another exemplary system for outputtingheart sounds.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the presentinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent invention, and it is to be understood that the embodiments maybe combined, or that other embodiments may be utilized and thatstructural, logical and electrical changes may be made without departingfrom the spirit and the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined by the appended claimsand their equivalents.

Referring to FIG. 1, an exemplary system 100 for outputting heart soundsin accordance with one embodiment of the present invention comprises animplantable system 102 and an external system 104. Implantable system102 and external system 104 are configured to communicate via acommunications link 106. In one embodiment, link 106 usesradio-frequency (RF) signals. In another embodiment, link 106 usesoptical signals. These communications may support monitoring, diagnosticand configuration functions.

Implantable system 102 includes an implantable device 108 operativelycoupled to a patient's heart 110 by a pacing lead 112. The components ofimplantable device 108 include an atrial sense amplifier 114, aventricular sense amplifier 116, an atrial stimulating circuit 118, aventricular stimulating circuit 120, a controller 122, a memory 124, anaccelerometer 126, an analog pre-processing circuit 128, ananalog-to-digital (A/D) converter 130, and an input/output (I/O)interface 132. The components of implantable device 108 are housedwithin an implantable housing (indicated by the broken lined box in FIG.1.) which is implanted within the patient's chest cavity (e.g., in thepectoral region).

Atrial sense amplifier 114, ventricular sense amplifier 116, atrialstimulating circuit 118 and ventricular stimulating circuit 120 areoperatively coupled to pacing lead 112 via a pair of conductors 134.Pacing lead 112 includes an atrial sensing electrode 136 and an atrialstimulating electrode 138 adapted to be disposed in the right atrialchamber of heart 110, and a ventricular sensing electrode 140 and aventricular stimulating electrode 142 adapted to be disposed in theright ventricular chamber of heart 110. Sensed atrial and ventricularelectrical signals generated by sensing electrodes 136 and 140 areapplied to atrial and ventricular sense amplifiers 114 and 116,respectively, and atrial and ventricular stimulating signals generatedby atrial and ventricular stimulating circuits 118 and 120 are appliedto atrial and ventricular stimulating electrodes 138 and 142,respectively. Atrial sense amplifier 114, ventricular sense amplifier116, atrial stimulating circuit 118, and ventricular stimulating circuit120, are each also operatively coupled to controller 122.

In other embodiments, other sensing electrode configurations are usedfor internally sensing one or more electrical signals of heart 110. Inone example, only one of sensing electrodes 136 and 140 is used. Inanother example, one or more electrodes placed within the body butoutside of heart 110 are used for generating sensed cardiac electricalsignals. In yet another example, a sensing electrode is placed withinthe implantable housing. In each of these examples, the sensingelectrodes are operatively coupled to controller 122.

In the embodiment shown in FIG. 1, the sensing electrodes 136 and 140and the stimulating electrodes 138 and 142 are disposed in the rightside of heart 110. In other embodiments, one or more sensingelectrode(s) and one or more stimulating electrode(s) are disposed inthe left side of the heart (in lieu of being disposed in the right sideof the heart, or in addition to sensing electrode(s) and stimulatingelectrode(s) disposed in the right side of the heart). The addition ofleft heart sensing may advantageously allow for the resolution ofambiguities due to disassociation of right and left heart conduction.

Controller 122 includes a micro-controller or microprocessor which isconfigured to execute a program stored in a read-only memory (ROM)portion of memory 124, and to read and write data to and from a randomaccess memory (RAM) portion of memory 124. By executing the programstored in memory 124, controller 122 is configured to process the atrialand ventricular electrical signals from atrial and ventricular senseamplifiers 114 and 116, and to provide control signals to atrial andventricular stimulating circuits 118 and 120. In response, stimulatingcircuits 118 and 120 provide stimulating pulses to heart 110 via atrialand ventricular stimulating electrodes 138 and 142 at appropriate times.In other embodiments, controller 122 may include other types of controllogic elements or circuitry.

Implantable device 108 may be referred to as a dual-chamber pacemakersince pacemaking functions are provided to both atrial and ventricularchambers of heart 110. In another embodiment, the implantable systemincludes a single-chamber pacemaker that senses electrical signals andprovides stimulating pulses to a single chamber of heart 110. In yetanother embodiment, the implantable system does not provide anystimulation of heart tissues, but includes one or more sensingelectrodes for sensing one or more electrical signals of heart 110, andfor providing corresponding sensed signals to controller 122. In stillanother embodiment, the implantable system does not provide any sensingelectrodes for sensing any cardiac electrical signals, but is configuredto sense and transmit signals representing heart sounds using a sensorsuch as accelerometer 126, as described below.

In the remainder of this description, implantable device 108 isdescribed as a dual-chamber pacemaker since the present system may beused with patients who have already had a pacemaker implanted in theirbodies, thereby alleviating the need to implant a device solely for thepurpose of monitoring heart sounds and/or intra-cardial electricalsignals. It is to be understood, however, that implantable system 102need not provide the stimulation functions described herein, and mayprovide other functions which are not described herein.

Accelerometer 126 is configured to provide sensed signals to analogpre-processing circuit 128, which generates an analog output signalwhich is digitized by A/D converter 130. The digitized accelerometersignal is received by controller 122. In the embodiment of FIG. 1,accelerometer 126 is located internally to the housing of implantabledevice 108. In another embodiment, accelerometer 126 is locatedexternally to the implantable housing. Accelerometer 126 may include,for example, a piezo-electric crystal accelerometer sensor of the typeused by pacemakers to sense the level of activity of the patient, or mayinclude other types of accelerometers that are packaged to fit in theimplantable housing. To detect heart sounds, other types ofsound-detecting sensors or microphones may also be used, such aspressure sensors or vibration sensors configured to respond to soundsmade by the heart.

In another embodiment, system 100 includes a plurality (two or more) ofsound-detecting sensors. In this embodiment, the plurality of sensedheart sound signals from the plurality of sensors may be individuallytransmitted to external system 104 for display as individual traces, maybe combined (e.g., averaged) by external system 104 before beingdisplayed as a single trace, or may be combined by controller 122 beforebeing transmitted to external system 104 as a single heart sound signal.These sensors may include different types of sensors, sensors that arelocated in different locations, or sensors that generate sensed signalswhich receive different forms of signal processing.

In one embodiment, accelerometer 126 is configured to generate sensedsignals representative of two distinct physical parameters: (1) thelevel of activity of the patient; and (2) the heart sounds generated byheart 110. Accordingly, analog pre-processing circuit 128 is configuredto pre-process the sensed signals from accelerometer 126 in a mannerwhich conforms to the signal characteristics of both of these physicalparameters. For example, if the frequencies of interest for measuringthe patient's level of activity are below 10 Hz, while the frequenciesof interest for detecting heart sounds are between 0.05 Hz and 50 Hz,then analog pre-processing circuit 128 may include a low-pass filterhaving a cutoff frequency of 50 Hz. Controller 122 may then performadditional filtering in software using, for example, a low-pass filterwith a cutoff frequency of 10 Hz to detect the level of activity of thepatient, and a band-pass filter with cutoff frequencies of 0.05 Hz and50 Hz to detect the heart sounds, although these signal processingfunctions could also be performed by external system 104. Along withfiltering, analog pre-processing circuit 128 may perform otherprocessing functions including automatic gain control (AGC) functions.

In another embodiment, implantable device 108 has two pre-processingchannels for receiving sensed signals from accelerometer 126. In stillanother embodiment, implantable device 108 includes two accelerometers,with one accelerometer configured to generate sensed signalsrepresentative of the level of activity of the patient and the otheraccelerometer configured to generate sensed signals representative ofheart sounds. In these latter two embodiments, any hardware and/orsoftware processing performed on the sensed signals can conform to thespecific characteristics of the respective sensed signals. For example,the analog pre-processing circuit used for the level-of-activity sensedsignals can provide a low-pass filter with a cutoff frequency of 10 Hz,while the analog pre-processing circuit for the heart-sound sensedsignals can provide a band-pass filter with cutoff frequencies of 0.05and 50 Hz. In the latter case, each accelerometer can be selected,located and/or oriented to maximize the detection of the respectivephysical parameter. In yet another embodiment, if the implantable devicedoes not need to sense the level of activity of the patient,accelerometer 126 may measure only the sounds made by heart 110.

Controller 122 is capable of bi-directional communications with externalsystem 104 via I/O interface 132. In one embodiment, I/O interface 132communicates using RF signals. In other embodiments, I/O interface 132communicates using optical signals, or a combination of RF and opticalsignals (e.g., RF signals for receiving data from external system 104and optical signals for transmitting data to external system 104, orvice-versa). Controller 122 uses I/O interface 132 for bi-directionalcommunications with external system 104 to support conventionalmonitoring, diagnostic and configuration pacemaker functions. Controller122 also uses I/O interface 132 to telemeter data representative of theheart sounds sensed by accelerometer 126 to external system 104. Invarious embodiments, controller 122 further uses I/O interface 132 totelemeter data representative of cardiac electrical signals (i.e.,electrogram or EGM signals), which may include data representative ofatrial electrical signals (i.e., A EGM signals) sensed by atrial sensingelectrode 136, and/or data representative of ventricular electricalsignals (i.e., V EGM signals) sensed by ventricular sensing electrode140. Thus, implantable system 102 is capable of sensing heart sounds,atrial electrical signals and ventricular electrical signals, and oftelemetering data representative of the heart sounds and/or cardiacelectrical signals to external system 104. In other embodiments,controller 122 telemeters data representative of cardiac electricalsignals which were sensed by other configurations of internal cardiacsensing electrodes.

In one embodiment, external system 104 includes an external device 142and a surface electrocardiograph (ECG) system 144. External device 142includes an external controller 146, an I/O interface 148, user inputdevice(s) 150, and user output device(s) 152. Using I/O interface 148,external controller 146 is configured for bi-directional communicationswith implantable device 108, for receiving input signals from inputdevice(s) 150, and for applying control signals to output device(s) 152.Input device(s) 150 include at least one input device which allows auser (e.g., a physician, nurse, medical technician, etc.) to generateinput signals to control the operation of external device 142, such asat least one user-actuatable switch, knob, keyboard, pointing device(e.g., mouse), touch-screen, voice-recognition circuit, etc. Outputdevice(s) 152 include at least one display device (e.g., CRT, flat-paneldisplay, etc.), audio device (e.g., speaker, headphone), or other outputdevice which generates user-perceivable outputs (e.g., visual displays,sounds, etc.) in response to control signals. External controller 146 isconfigured to receive the data representative of heart sounds, atrialelectrical signals and/or ventricular electrical signals fromimplantable system 102, and to generate control signals that, whenapplied to output device(s) 152, cause the output device(s) to generateoutputs that are representative of the heart sounds, the atrialelectrical signals and/or the ventricular electrical signals.

Surface ECG system 144 includes electrodes adapted to be electricallycoupled to the surface of the patient's chest for sensing cardiacelectrical signals, and is configured to produce ECG output signalswhich are coupled to I/O interface circuit 148. External controller 146is configured to receive the ECG signals from I/O interface circuit 148,and to generate control signals which, when applied to output device(s)152, cause the output device(s) to also generate outputs representativeof the patient's ECG. Alternatively, in other embodiments, surface ECGelectrodes are coupled directly to external device 142, rather thanbeing supplied by a surface ECG system. In another embodiment, externaldevice 142 does not receive surface ECG signals, and does not outputsuch ECG signals. (Note: “ECG” is used herein to refer to cardiacelectrical signals measured from the surface of the body, and “EGM” isused to refer to internally-measured cardiac electrical signals.)

In one embodiment, external device 142 comprises an external programmingdevice for a cardiac pacemaker, such as the ZOOM™ external programmeravailable from the Guidant Corporation, except that the externalprogrammer is configured (i.e., programmed or otherwise set up) toperform the various functions described in the present application.

In one embodiment, system 100 further includes a remote system 154operatively coupled to communicate with external system 104 viatransmission media 156. Remote system 154 includes one or more userinput device(s) 158, and one or more user output device(s) 160, whichallow a remote user to interact with remote system 154. Transmissionmedia 156 includes, for example, a telephone line, electrical or opticalcable, RF interface, satellite link, local area network (LAN), wide areanetwork (WAN) such as the Internet, etc. Remote system 154 cooperateswith external system 104 to allow a user located at a remote location toperform any of the diagnostic or monitoring functions that may beperformed by a user located at external system 104. For example, datarepresentative of heart sounds and/or cardiac electrical signals arecommunicated by external system 104 to remote system 154 viatransmission media 156 to provide a visual display and/or an audiooutput on output device(s) 160, thereby allowing a physician at theremote location to aid in the diagnosis of a patient. System 154 is“remote” in the sense that a user of remote system 154 is not physicallycapable of actuating input device(s) 150 and/or of directly perceivingoutputs generated by output device(s) 152. For example, system 154 maybe located in another room, another floor, another building, anothercity or other geographic entity, across a body of water, at anotheraltitude, etc., from external system 104.

Referring to FIG. 2, in one embodiment, the processing 200 performed bycontroller 122 of implantable device 108 includes detecting heart soundsby receiving sensed signals representative of the heart sounds fromaccelerometer 126 (at 202), detecting atrial electrical signals byreceiving sensed signals representative of the atrial electrical signalsfrom atrial sensing electrode 136 (at 204), detecting ventricularelectrical signals by receiving sensed signals representative of theventricular electrical signals from ventricular sensing electrode 140(at 206), and transmitting data representative of the heart sounds,atrial electrical signals, and ventricular electrical signals toexternal device 142 (at 208).

In another embodiment, processing 200 further includes signal processingthe accelerometer, atrial and ventricular sensed signals to generateprocessed sensed signals (between 206 and 208), and then transmittingthe processed sensed signals to external device 142 (at 208). The signalprocessing may also be performed on only one or two of these sensedsignals. However, performing the signal processing in implantable device108 (rather than in external device 142, as described below relative toFIG. 3) may increase the computational requirements for implantabledevice 108, and may also increase the transmission load between devices108 and 142. It is to be understood that the division of signalprocessing between implantable device 108 and external device 142 couldbe modified from that disclosed herein, as would be apparent to a personof skill in the art.

In another embodiment, processing 200 also includes storing one or moreof the raw or processed sensed signals in memory 124 for later retrievalby external device 142. In still another embodiment, the processingperformed by controller 122 does not include detecting the atrialelectrical signals (at 204) and/or the ventricular electrical signals(at 206), in which case the corresponding EGM data is not transmitted toexternal device 142 (at 208). In yet another embodiment, the processingperformed by controller 122 includes detecting other cardiac electricalsignals sensed by other cardiac electrical signal sensors, andtransmitting data representative of these other cardiac signals toexternal device 142.

Referring to FIG. 3, in one embodiment, the processing 300 performed byexternal controller 146 of external device 142 includes receiving thedata representative of the heart sounds, atrial electrical signals andventricular electrical signals from implantable device 108 (at 302),receiving surface ECG data from surface ECG system 144 or directly fromsurface ECG leads (at 304), processing the accelerometer, atrialelectrical signals, ventricular electrical signals and surface ECG data(at 306), and generating output control signals to simultaneously outputthe raw and/or processed accelerometer, atrial electrical signals,ventricular electrical signals, and surface ECG signals on outputdevice(s) 152 (at 308). Processing 300 may also include receiving timingcomparison command signals from input device(s) 150 (at 310), andgenerating control signals to output timing comparison information onoutput device(s) 152 (at 312). Processing 300 may also include storingone or more of the raw or processed sensed signals in memory for lateranalysis.

In other embodiments, the processing performed by external controller146 does not include receiving the atrial and/or ventricular electricalsignals (at 302), or receiving surface ECG data (at 304), in which casethe corresponding EGM data or surface ECG data is not processed (at 306)or output (at 308). Further, it is contemplated that external controller146 may not perform any processing of the accelerometer, atrialelectrical signals and/or ventricular electrical signals (at 306), andmay instead receive corresponding processed data (rather than raw data)from implantable device 108. The processing of these signals (at 306) isillustrated in FIG. 3, however, to indicate that the processingdescribed below in relation to FIG. 4 may well be performed by externaldevice 142 rather than implantable device 108, thereby reducing thecomputational requirements for implantable device 108.

Referring to FIG. 4, the signal processing 400 performed on the heartsound data by external controller 146 in accordance with one embodimentof the invention is shown. In other embodiments, some or all of thissignal processing could instead be performed by controller 122 ofimplantable device 108, or by either external or implantable hardware.Signal processing 400 includes a first processing path 402 used formachine detection of heart sounds, and a second processing path 404 usedfor visual display of heart sounds. Alternatively, only one of heartsound signal processing paths 402 and 404 is provided.

First processing path 402 includes a band-pass filter 406, a rectifier408, a low-pass filter 410, and an ensemble averager 412, coupled inseries. Raw accelerometer data 414 (representative of the heart sounds)is applied to band-pass filter 406, which has lower and upper cutofffrequencies set to pass frequencies indicative of heart sounds, toproduce band-pass filtered data 416. In one example, the lower and uppercutoff frequencies are 0.05 Hz and 50 Hz, respectively. The cutofffrequencies are also set to reject frequencies due to movement of thepatient (e.g., walking around, muscle twitches, etc.) to the extent thatthe heart sound signals still pass. Band-pass filtered data 416 is thenapplied to rectifier 408 to produce rectified data 418 that is, in turn,applied to low-pass filter 410 to produce filtered data 420. In oneexample, the cutoff frequency for low-pass filter 410 is 10 Hz.

Filtered data 420 is applied to ensemble averager 412 to produceprocessed accelerometer data 422, which is used for machine detection ofheart sounds. Ensemble averager 412 is triggered by an output 424 of asystole detector 426, which is asserted to open a window of interestwhen the start of a cardiac cycle is detected based upon the electricalsystole (which may be detected using the A EGM, V EGM and/or surface ECGsignals). Ensemble averager 412 causes the repetitive heart sound datato be averaged over a number of cardiac cycles to accentuate the heartsounds (which are correlated to a particular frequency) while filteringout random or spurious noise (which are not correlated to a particularfrequency). For example, ensemble averager 412 may average sequentialheart sounds over a period of between 2 and 128 cardiac cycles, althoughother periods may also be used. In other embodiments, heart sounds aresequentially averaged over a period of time (e.g., one minute), or overthe course of an event or condition (e.g., while the patient isperforming an exercise), in which case only completed cardiac cycleswill be averaged. Note that signal averaging the heart sound dataincludes the superposition and the summation of successive temporalsamples of the pulsatile heart sound waveform.

Second processing path 404 includes a band-pass filter 428 and anensemble averager 430, coupled in series. Raw accelerometer data 414(representative of the heart sounds) is applied to band-pass filter 428,which has lower and upper cutoff frequencies set to pass frequenciesindicative of heart sounds, to produce band-pass filtered data 432. Inone example, the lower and upper cutoff frequencies are 0.05 Hz and 50Hz, respectively. The cutoff frequencies are also set to rejectfrequencies due to patient movement to the extent that the heart soundsignals still pass. Band-pass filtered data 432 is then applied toensemble averager 430 to produce processed accelerometer data 434, whichis used for visual display of heart sounds. Ensemble averager 430 istriggered by output 424 of systole detector 426, which is asserted toopen a window of interest when the start of a cardiac cycle is detectedbased upon the electrical systole. Ensemble averager 430 causes theheart sound data to be averaged over a number of cardiac cycles (e.g.,between 2 and 128 cardiac cycles, or other range) to accentuate theheart sounds while filtering out random or spurious noise. Byeliminating the rectifier and low-pass filter of processing path 402,processing path 404 avoids eliminating information from the visualdisplay of the heart sound data which may be useful to a physician,nurse, medical technician or other user of system 100.

In one embodiment, ensemble averager 430 includes logic to reject datafrom cardiac cycles outside the range of normal as such cycles may be ofnon-physiologic origin (e.g., PVC's). However, in the case of frequentPVC's, the PVC interval may become the norm. Thus, this logic may beadaptive so as to include such PVC's.

The signal processing for the heart sound data illustrated in FIG. 4 ismerely exemplary, and other types of signal processing may be used. Forexample, the cutoff frequencies described above for the band-pass andlow-pass filters may be varied, one or both of these filters may beeliminated, or other filters may be added. In one embodiment, the rawaccelerometer data could be applied directly to an ensemble averager.

Referring to FIG. 5, an exemplary output screen display 500 generated byexternal device 142 on an output device 152 is shown. In this example,it is assumed implantable system 102 includes accelerometer 126, atrialsensing electrode 136, and ventricular sensing electrode 140, and thatimplantable system 102 transmits the raw sensed signals from each ofthese sensors to external device 142. It is also assumed that externaldevice 142 generates display control signals that are output to adisplay to generate these outputs.

Output screen display 500 includes multiple horizontal traces, includinga surface ECG trace 502, a raw accelerometer trace 504, a processedaccelerometer trace 506, an atrial electrical signal (“A EGM”) trace508, and a ventricular electrical signal (“V EGM”) trace 510.Alternatively, one or more of traces 502-510 may not be displayed. Forexample, since raw accelerometer trace 504 includes a relatively largeamount of noise, this trace may not be displayed since it may not beeasily interpreted by a user. Thus, display 500 simultaneously shows avisual trace of all five of these signals, which may be used by a user(e.g., a physician) to diagnose an electrical/mechanical disassociationof heart 110. Note that, if it is desirable for a user at a remotelocation to aid in the diagnosis of heart 110, the data representativeof the heart sounds and electrical signals may be communicated byexternal device 142 to remote system 154 for display on one of outputdevice(s) 160.

In one embodiment, display 500 includes one or more traces fordisplaying one or more cardiac electrical signals that were sensed fromthe left side of the heart, such as an “LV EGM” signal sensed by asensing electrode disposed in the left ventricle.

In one embodiment, to help the user determine timing relationshipsbetween the signals shown in FIG. 5, external system 142 (and/or remotesystem 154) generates timing comparison control signals which, whenapplied to the display device, cause the display device to output timingcomparison information indicating timing between the displayed signals.For example, system 142 (and/or system 154) may generate control signalswhich cause the display device to display a pair of vertical lines orcalipers 512A and 512B, which can be moved horizontally by the user viaa pair of input devices 150 (or input devices 158), with each inputdevice controlling the position of one caliper. The calipers can helpthe user to compare timing between any of the displayed signals. Tofurther aid the user, external system 142 (and/or remote system 154) maycause the display device to display a visual indicia 160 indicating thetime period between the calipers. For example, indicia 160 indicatesthat the distance between calipers 512A and 512B represents 50 msec.

In one embodiment, to further aid the user in interpreting the display,heart sound data is automatically processed to identify one or moreheart sounds, and visual indicia indicative of the identified sounds arealso displayed on display 500. For example, external controller 146 mayautomatically process the sensed accelerometer data (e.g., processedaccelerometer data 422) to detect the S1 and S2 heart sounds (andpossibly the S3 heart sound), and to generate the display controlsignals so as to cause visual indicia (e.g., “S1” and “S2”) to bedisplayed in association with the locations of the heart sounds onprocessed accelerometer trace 506 (or on raw accelerometer trace 504),as in FIG. 5. The S1 heart sound is associated with the closure of theAV valve and opening of the aortic valve in the heart, the S2 heartsound is associated with the subsequent closure of the aortic valve, andthe S3 heart sound (less pronounced than the S1 and S2 sounds) isassociated with the end of the heart's fast-filling phase duringdiastole. An exemplary method for automatically processing accelerometersignals to detect S1, S2 and S3 heart sounds is disclosed in U.S. Pat.No. 5,792,195, issued to Carlson et al. on Aug. 11, 1998, andincorporated by reference herein in its entirety. The heart soundindicia may help users to quickly and accurately identify these sounds,and may be especially helpful to less experienced users.

In one embodiment, to provide still additional aid to the user, theintra-cardiac EGM and/or surface ECG data may be automatically processedto identify one or more electrical cardiac events, and visual indiciaindicative of the identified events may be displayed on display 500. Forexample, external controller 146 may be configured to automaticallyprocess the sensed atrial electrical data, ventricular electrical data,and/or surface ECG data to identify the P waves, QRS complexes, T waves,U waves, or other electrical cardiac events, and to generate the displaycontrol signals so as to cause visual indicia (e.g., “P”, “QRS”, “T”,“U”, etc.) to be displayed in association with the locations of thecorresponding events on A EGM trace 508, V EGM trace 510, and/or surfaceECG trace 502. The electrical cardiac event indicia may help users toquickly and accurately identify the electrical cardiac events, and maybe especially helpful to less experienced users. External controller 146may also provide additional processing (e.g., filtering) of the A EGM, VEGM and/or surface ECG signal to further delineate the events ofinterest (e.g., by low-pass filtering these signals to eliminateeverything but the higher signal peaks).

To provide the user with additional operational control, the generationof the heart sound indicia and/or electrical cardiac event indicia ondisplay 500 may be controlled by one or more of input devices 150 (orinput devices 158). For example, a first input device (e.g., a switch)may be provided to allow the user to turn the heart sound indicia on oroff, and a second input device may be provided to turn the electricalevent indicia on or off.

In other embodiments, external device 142 performs additional processingto aid the user in interpreting display 500. For example, in oneembodiment, external device 142 automatically calculates timingdifferences (e.g., electrical-to-mechanical time delay) for each heartbeat, and outputs (e.g., lists, plots, etc.) the timing differences on abeat-to-beat basis. The user can examine the outputs to determine howthe electrical-to-mechanical time delay changes over time (e.g., over anumber of heart beats). In situations where electrical-to-mechanicaldisassociation occurs only in limited circumstances (e.g., when thepatient is exercising), showing such timing differences over time may beuseful to a physician.

In another embodiment, external controller 146 calculates and displaystiming differences between automatically detected cardiac events, suchas between automatically detected heart sounds, between automaticallydetected heart sounds and electrical cardiac events, betweenautomatically detected electrical cardiac events, etc. For example,external controller 146 may calculate timing differences between the S1and S2 heart sounds, between the QRS complex and S1 heart sound, orbetween the P wave and QRS complex, and then generate output controlsignals to cause visual indicia indicative of these timing differences(e.g., “n msec”) to be displayed on display 500. In one embodiment, thetiming differences that are displayed on display 500 are selected by theuser based upon input signals generated by user input device(s) 150 (orinput device(s) 158). In one example, a user employs a mouse to select aparticular timing interval from a pull-down list of timing intervalsthat he or she would like to see calculated and displayed on display500.

In one embodiment, one or more of output devices 152 (or output devices160) comprises an audio device for generating audio outputsrepresentative of the heart sounds. For example, raw accelerometer data414 may be applied to a speaker to allow the user to hear and identifyheart abnormalities. Alternatively, processed accelerometer data, suchas processed accelerometer data 422 or 434, may be applied to an audiodevice to allow the user to hear and identify heart abnormalities. Othertypes of processed accelerometer data, including filtered andsignal-averaged accelerometer data, may also be applied to an audiodevice to allow the user to hear and identify heart abnormalities. Ineach case, the user is presented with the heart sounds in the audiodomain, which may more familiar to a physician or other user who is usedto listening to heart sounds using a stethoscope. In each case, the usermay also be presented with any or all of the traces shown in FIG. 5,such that the user may receive cardiac information in both the visualand the audio domains.

Referring to FIG. 6, another exemplary output screen display 600generated by external device 142 on an output device 152 is shown. Inthis example, it is again assumed that implantable system 102 includesaccelerometer 126, atrial sensing electrode 136, and ventricular sensingelectrode 140, that implantable system 102 transmits the raw sensedsignals from each of these sensors to external device 142, and thatexternal device 142 generates display control signals that are output toa display to generate these outputs. The displayed traces include aprocessed accelerometer trace 602, an atrial electrical signal (“A EGM”)trace 604, and a ventricular electrical signal (“V EGM”) trace 606.Other traces, such as a surface ECG trace and/or a raw accelerometertrace, could also be displayed.

In this embodiment, to help the user determine timing relationshipsbetween the traces shown in FIG. 6, external device 142 (and/or remotesystem 154) is configured to generate timing comparison control signalswhich cause the display device to vertically move one or more of thetraces under the control of the user via one or more of input devices150 (or input devices 158). For example, each input device may controlthe vertical position of one trace. By vertically moving one or more ofthe traces, the user can superimpose the traces over one another to showtiming comparisons. For example, as illustrated by the dashed lines inFIG. 6, the user has used an input device 150 to move A EGM trace 604upward to superimpose this trace over processed accelerometer trace 602.By doing so, timing comparisons between traces 602 and 604 becomereadily apparent. Thus, in this embodiment, visual outputs of heartsounds may be superimposed over visual outputs of cardiac electricalsignals to show timing comparisons therebetween. Note that, sincedisplay 600 does not indicate which superimposed signal was moved “over”another, superimposing trace A “over” trace B is the same assuperimposing trace B “over” trace A.

Referring to FIG. 7, in another embodiment, implantable device 108includes an arrhythmia logbook feature. With this feature, if anarrhythmia (e.g., an abnormally fast heart rate) is detected,implantable device 108 records data in memory for later examination by aphysician for use in making a diagnosis. Implantable device 108 may, forexample, continually record 10 seconds of data in an area of memory 124,and may simply rewrite over that area of memory. If, however, anarrhythmia is detected (e.g., the V EGM signal indicates that heart 110is beating at an abnormally high rate of 180 beats/minute), the 10seconds of recorded data is saved in another area of memory 124, alongwith an additional 20 seconds of data recorded after the arrhythmia.Other arrhythmia events may also be logged. Then, on the next visit ofthe patient to a doctor, the doctor can use external device 142 to readthe data from the logbook, and can examine the data to look forarrhythmia events. For example, the logbook may indicate that, in thethree months since the patient was last seen, heart 110 experienced fiveepisodes of fast atrial heart beat, three atrial flutters, and oneventricular fibrillation. The data recorded by implantable device 108 inassociation with each arrhythmia event may include heart rate data, AEGM data, V EGM data and, in accordance with the present system, rawand/or processed heart sound data.

To provide the arrhythmia logbook feature, in one embodiment, controller122 of implantable device 108 performs the processing 700 shown in FIG.7. In particular, controller 122 detects heart sounds by receivingsensed signals representative of the heart sounds from accelerometer 126(at 702), detects atrial electrical signals by receiving sensed signalsrepresentative of the atrial electrical signals from atrial sensingelectrode 136 (at 704), detects ventricular electrical signals byreceiving sensed signals representative of the ventricular electricalsignals from ventricular sensing electrode 140 (at 706), and stores theaccelerometer, atrial EGM and ventricular EGM data in memory 124 (at708). In one embodiment, controller 122 continually stores 10 seconds ofsuch data (along with other desired data, such as heart rate data) in aparticular area of memory 124. If controller 122 determines that anarrhythmia has not occurred (at 712) and that no arrhythmia logbookplayback request has been received from external device 142 (at 714),controller 122 loops back (to 702), and repeats these operations. As newdata is collected and stored in memory 124, the oldest data isre-written by the new data such that the particular area of memoryalways stores the last 10 seconds of data. If an arrhythmia is detected(at 712), however, controller 122 creates a record in another area ofmemory (i.e., the arrhythmia logbook), and copies the last 10 seconds ofdata into that record. Then, for the next 20 seconds, controller 122continues to monitor data, and stores this data within that same record.Thus, for each detected arrhythmia, controller 122 creates a record inmemory 124 that contains data for the 10 seconds leading up to thearrhythmia, and the 20 seconds after the arrhythmia. In otherembodiments, less than or more than this amount of data is stored eitherbefore or after each arrhythmia occurs. Then, when controller 122determines that an arrhythmia logbook playback command is received fromexternal device 142, controller 122 transmits the records from memory124 to external device 142. External device 142 then outputs the datafrom these records to output device(s) 152 (or output device(s) 160).The physician can then examine the recorded data for each arrhythmia toaid in making a diagnosis. Thus, by using the arrhythmia logbook featureof the system, the physician is provided with heart sound informationfrom both before and after the arrhythmia.

In one embodiment, system 100 may provide more sophisticated signalprocessing in cases of cardiac arrhythmia. For example, in the case ofbigeminy, system 100 may be configured to use two averaging processes inorder that like events are averaged separately. Exemplary signalprocessing techniques that could be employed by system 100 include, forexample, those described in U.S. Pat. Nos. 4,799,493, 4,799,486,4,793,361 and 4,721,114. In another embodiment, implantable device 108may be configured to detect heart murmurs or extra heart sounds, tocount such extra heart sounds, and to transmit such counts to externaldevice 142 for output on one of output device(s) 150 (or devices 160).

Referring to FIG. 8, an exemplary system 800 for outputting heart soundsaccording to another embodiment comprises an implantable device 802coupled to a patient's heart (not shown) by a pacing lead 804 and one ormore heart electrode(s) 806, and operatively coupled to an externaldevice (not shown) via a communications link 808. In one embodiment,heart electrode(s) 806 includes an atrial sensing electrode, ventricularsensing electrode, atrial stimulating electrode and ventricularstimulating electrode as in FIG. 1.

Implantable device 802 includes one or more cardiac sense amplifier(s)810 and one or more cardiac stimulating circuit(s) 812 operativelycoupled to heart electrode(s) 806 via lead 804. In another embodiment,where device 802 does not provide heart stimulation, device 802 does notinclude cardiac stimulating circuit(s) 812. Device 802 also includes acontroller 814, a memory 816 operatively coupled to controller 814, anactivity level detecting path 818, a heart sound detecting path 820, asystole detector 822, and an I/O interface 824. Activity level detectingpath 818 includes an activity level sensor 826 for sensing patientactivity, an analog pre-processing circuit 828 for pre-processingsignals generated by activity level sensor 826, an A/D converter 830 fordigitizing the activity level signals, and an activity level filter 832for filtering the digitized signals to eliminate sources of noise suchas those caused by heart sounds. Heart sound detecting path 820 includesa heart sound sensor 834 for sensing heart sounds, an analogpre-processing circuit 836 for pre-processing signals generated by heartsound sensor 834, A/D converter 830 for digitizing the heart soundsignals (e.g., using a different channel than the channel used for theactivity level signals), a heart sound filter 838 for filtering thedigitized signals to eliminate sources of noise such as those caused bypatient activity, an S1 heart sound detector 840 for detecting the S1heart sound, an S2 heart sound detector 842 for detecting the S2 heartsound, and an S3 heart sound detector 844 for detecting the S3 heartsound. Controller 814 transmits data representing the patient's activitylevel and the S1, S2 and S3 heart sounds to the external device via I/Ointerface 824. Where S1, S2 and S3 heart sound detectors 840, 842 and844 ensemble average the heart sound signals, controller 814 provides anoutput signal indicative of the start of a cardiac cycle from systoledetector 822 to heart sound detectors 840, 842 and 844 for use as atrigger. In one embodiment, the outputs from S1, S2 and S3 heart sounddetectors 840-844 comprise a sequence of pulses, each pulse representinga detected heart sound. The external device receives the heart sound andcardiac electrical signal data via link 808, and simultaneously outputsthis data.

In one embodiment, activity level filter 832, heart sounds filter 838,heart sound detectors 840-844 and systole detector 822 are implementedby controller 814 through appropriate programming commands. In anotherembodiment, one or more of filters 832 and 838, and detectors 840-844,822, are implemented by one or more hardware circuits. In anotherembodiment, some or all of the processing functions of FIG. 8 areperformed by the external device instead of device 802. In anotherembodiment, system 800 includes S1 and S2 detectors 840 and 842, butdoes not include S3 detector 844. In another embodiment, system 800includes other sound detectors for detecting other heart sounds. Inanother embodiment, when an electrical-mechanical disassociation isdetected, stimulation timing provided by stimulating electrodes 138 and142 is changed.

CONCLUSION

Thus, exemplary embodiments of an improved apparatus and method foroutputting heart sounds, and/or for comparing electrical operation ofthe heart to mechanical operation of the heart, are disclosed herein.The disclosed apparatus and method for outputting heart sounds do notrequire the use of a stethoscope placed on the body of the patient, andare not subject to various factors which affect the heart sounds heardusing a stethoscope. The disclosed apparatus and method for comparingelectrical and mechanical operations of the heart also do not requirethe use of a stethoscope, are not subject to various factors whichaffect the heart sounds heard using a stethoscope, do not require ECGprobes to be electrically coupled to the patient's chest, increase theaccuracy of comparisons between heart sounds and electrical signals,decrease the level of skill needed to identify electrical-mechanicaldisassociation, provide for continuous monitoring of suchelectrical-mechanical disassociation, and are capable of producing awritten record showing such disassociation.

As indicated above, the outputs generated by system 100 may be used by aphysician to diagnose problems with heart 110 such aselectrical-mechanical disassociation, or problems leading to cardiacarrhythmia. The outputs may also be used by a physician located remotelyfrom the patient to diagnose the patient by checking the patient's heartsounds through a telephone, Internet or other communication connection.The sensed heart sound signals generated by system 100 may also be usedfor other purposes. For example, the heart sound signals may be usefulin optimization of timing for CHF pacing, for determining the best AVdelay, or for identifying the upper rate limit for a pacemaker.

Also, while the above description has focused on the relative timing ofthe various cardiac signals, the morphology or amplitude of the heartsound and cardiac electrical signals may also provide diagnosticinformation. For example, a heart sound signal with an amplitude lowerthan normal may be suggestive of certain heart abnormalities.

The above description is intended to be illustrative, and notrestrictive. Many other embodiments will be apparent to those ofordinary skill in the art upon reviewing the present specification. Forexample, the implantable device described herein need not be a cardiacpacemaker, but may be another type of implantable device. Also, theexternal device described herein need not be an external pacemakerprogrammer, but may be another type of external device such as a cardiacmonitor. The processing described herein as being performed by externalcontroller 146 may also be performed by the implantable device, or byother combinations of hardware and software. Other signal processingroutines may also be used. Further, while the system described hereinoutputs heart sounds, A EGM, V EGM and surface ECG signals, one or moreof these signals need not be output, or may be replaced by the output ofanother internal or external cardiac signal. The scope of the presentinvention should therefore be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

1. An external system for communicating with an implanted system,comprising: an interface circuit configured to communicate with theimplanted system; an output device configured to generate outputsrepresentative of heart sounds detected by the implantable system inresponse to control signals, the outputs including visual display of theheart sounds; and a control circuit, coupled to the interface circuitand the output device, to receive data representative of the heartsounds from the implanted system and generate the control signals, thecontrol circuit configured to apply the data representative of the heartsounds to a first processing path configured for machine detection ofthe heart sounds using the data representative of the heart sounds and asecond processing path configured for the visual display of the heartsounds.
 2. The external system of claim 1, wherein the interface circuitis configured to communicate with the implanted system using opticalsignals.
 3. The external system of claim 1, wherein the output devicecomprises an audio device configured to generate audio outputsrepresentative of the heart sounds.
 4. The external system of claim 1,wherein the first processing path comprises a first band-pass filter, arectifier, a low-pass filter, and a first ensemble averager, and thesecond processing path comprises a second band-pass filter and a secondensemble averager.
 5. The external system of claim 4, wherein thecontrol circuit is configured to trigger the first ensemble averager andthe second ensemble averager using detection of systole.
 6. The externalsystem of claim 1, wherein the output device is configured to generateoutputs representative of the heart sounds and one or more cardiacelectrical signals in response to the control signals, and wherein thecontrol circuit is configured to receive the one or more cardiacelectrical signals and generate the control signals causing the outputdevice to generate the outputs representative of the heart sounds andthe one or more cardiac electrical signals.
 7. The external system ofclaim 6, wherein the output device is configured to generate outputsrepresentative of the heart sounds and a surface electrocardiograph(ECG) signal in response to the control signals, and wherein the controlcircuit is configured to receive the surface ECG signal and generate thecontrol signals causing the output device to generate the outputsrepresentative of the heart sounds and the surface ECG signal.
 8. Theexternal system of claim 7, wherein the control circuit is configured togenerate timing comparison control signals causing the output device tooutput timing comparison information indicative of relative timingbetween the heart sounds and surface ECG events.
 9. The external systemof claim 8, wherein the control circuit is configured to generate thetiming comparison control signals causing the output device to displaycalipers for indicating time intervals between the heart sounds and thesurface ECG events.
 10. The external system of claim 9, furthercomprising an input device coupled to the control circuit, the inputdevice configured for controlling the display of the calipers.
 11. Amethod for outputting heart sounds detected by an implantable system,comprising: receiving data representative of the heart sounds from theimplantable system; processing the data representative of the heartsounds using a first processing path configured for machine detection ofthe heart sounds using the data representative of the heart sounds and asecond processing path configured for visual display of the heartsounds; generating outputs representative of the heart sounds using theprocessed data representative of the heart sounds, the outputs includingthe visual display of the heart sounds presented on a display screen ofan external device communicatively coupled to the implantable system.12. The method of claim 11, wherein processing the data representativeof the heart sounds using the first processing path comprises processingthe data representative of the heart sounds using a first band-passfilter, a rectifier, a low-pass filter, and a first ensemble average forthe machine detection of the heart sounds, and processing the datarepresentative of the heart sounds using the second processing pathcomprises processing the data representative of the heart sounds using asecond band-pass filter and a second ensemble averager.
 13. The methodof claim 12, wherein receiving the data representative of the heartsounds from the implantable system comprises receiving the datarepresentative of the heart sounds from the implantable system usingoptical signals.
 14. The method of claim 12, further comprisinggenerating audio outputs representative of the heart sounds.
 15. Themethod of claim 12, comprising detecting systole, and triggering thefirst ensemble averager and the second ensemble averager using detectionof the systole.
 16. The method of claim 12, comprising: receiving one ormore cardiac electrical signals; and generating outputs representativeof the heart sounds and the one or more cardiac electrical signals. 17.The method of claim 16, further comprising generating and outputtingtiming comparison information indicative of relative timing between theheart sounds and cardiac electrical events.
 18. The method of claim 17,wherein generating and outputting timing comparison informationcomprises displaying calipers for indicating time intervals between theheart sounds and the cardiac electrical events.
 19. The method of claim18, wherein receiving the one or more cardiac electrical signalscomprises receiving one or more cardiac electrical signals from theimplantable system.
 20. The method of claim 18, wherein receiving theone or more cardiac electrical signals comprises receiving a surfaceelectrocardiograph (ECG) signal.